Abstract
In order to find out the effects of shading and nitrogen fertilization on the accumulation of $NO_3\;^-$ in leaves of lettuce, lettuce plants were cultivated in the pots under glasshouse condition with different rates of shading(0, 50%) and nitrogen fertilization(100, 180, 200, 300, $400\;kg{\cdot}ha^{-1}$). The pH value was lower in soil after experiment than before experiment, whereas, contents of EC and $NO_3-N$ were higher. As the amounts of nitrogen fertilization were increased, pHs were decreased, but EC and the contents of $NO_3-N$ were increased. At the nitrogen fertilizations of 100, 180, 200, 300 and $400\;kg{\cdot}ha^{-1}$, the germination rates of lettuce were decreased to 84, 78, 76, 72 and 74%, and survival rates were also decreased to 94, 94, 90, 60 and 46%, respectively. However, the fresh weight of lettuce was highest at $45\;g{\cdot}plant^{-1}$ in the recommended fertilizer $plot(180\;kg{\cdot}ha^{-1})$ with non-shading condition. The contents of $NO_3\;^-$ in the leaves of lettuce were increased 2.8-4.1 times under 50% shading conditions than that under non-shading condition. It kept increasing up to seven order of growth phase; however, it started to decrease after eight order phase. Nitrate reductase activity of lettuce in non-shading condition was higher than that in 50% shading condition.
차광 및 질소시비량이 상추의 엽내 $NO_3\;^-$ 축적에 미치는 영향을 구명하기 위하여 질소 시비량을 달리하여(100, 180, 200, 300, $400\;kg{\cdot}ha^{-1}$) 50% 차광 과 무차광 상태에서 상추를 재배하였다. 1. 시험전 토양에 비하여 시험후 토양에서 pH는 낮아진 반면 EC 및 $NO_3-N$ 함량은 높아졌다. 질소 시비량이 증가할수록 pH는 낮아지는 경향이며, EC 및 $No_3\;^-$ 함량은 높아지는 경향이었다. 또한, 시험후 토양에서 $NO_3-N$ 함량이 증가할 수록 EC가 높아졌다. 2. 질소시비량이 100, 180, 200, 300 그리고 $400kg{\cdot}ha^{-1}$에서 상추의 입모율은 각각 84, 78, 76, 72 및 74% 이었고, 생존율은 각각 94, 94, 90, 60 및 46%로서 질소시비량이 증가할수록 입모율 및 생존율이 감소하였다. 상추의 생산량은 무차광 재배에서 진단시비($180\;kg{\cdot}ha^{-1}$)에서 $45\;g{\cdot}$주$^1$ 로서 가장 높았다. 3. 상추 엽중 $NO_3\;^-$ 함량은 질소시비량이 증가할수록 높아졌고 또한 무차광에 비하여 50% 차광에서 $2.8{\sim}4.1$배 높았으며, 엽위별로의 $NO_3\;^-$ 함량은 7엽기까지 증가하다가 8엽기부터 감소하였다. 4. NRA은 50% 차광보다 무차광에서 높게 나타났다.
(Chungbuk Agricultural Research and Extension Services)
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